Fractionation of effluent from HF catalyzed alkylation

ABSTRACT

A depropanizer overhead from fractionation of an HF catalyzed isoparaffin-olefin alkylation is partially condensed to form a stream relatively poor in ethane and vapors relatively rich in ethane. The stream relatively poor in ethane is used as reflux and is pumped by a pump to a depropanizer-fractionator. Vapors rich in ethane are condensed, contacted with liquid HF and are used as feed to an HF stripping zone. Bottoms from the stripping zone consisting essentially of ethane and propane to be yielded from the operation are flashed to form overhead ethane and propane yield and a bottoms propane stream poor in ethane and lean in HF and said stream poor in ethane and lean in HF is used as flush for said pump. HF stripper overhead is at least in part condensed, two liquid phases are formed, the acid phase is removed and the hydrocarbon phase is returned as reflux to the stripper and/or the overhead is at least in part condensed and the condensate thus obtained intermingled with the condensate obtained when condensing the vapors rich in ethane; phases are formed, and acid phase formed is separated and hydrocarbon phase is used as feed to the stripping zone. A pump is provided to draw from an extractor-settler HF acid settled therein and to admix therewith either or both the condensates obtained upon condensing the ethane rich vapor and that obtained upon condensing HF stripper overhead, thus intermingled liquids are passed to said extractor-settler from which an acid phase formed is separated and hydrocarbon phase formed is passed to the stripping operation. Flush for the pump is provided by the propane lean in ethane and lean in HF.

[ 1 Dec. 30, 1975 FRACTIONATION OF EFFLUENT FROM HF CATALYZED ALKYLATION[75] Inventor: Charles C. Chapman, Bartlesville,

Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

[22] Filed: June 11, 1974 [21] Appl. No.: 478,226

[52] US. Cl 260/683.42; 260/683.48 [51] Int. Cl. C07C 3/54 [58] Field ofSearch 260/683.48, 683.42

[56] References Cited UNITED STATES PATENTS 2,894,999 7/1959 LawsonZoo/683.48 3,190,935 6/1965 Hutson, Jr. 260/683.42 3,763,265 10/1973Hutson, Jr., et al. 260/683.48 3,767,726 10/1973 Hutson, Jr., et al.260/683.48 3,804,918 4/1974 Henderson 260/683.48

Primary Examiner-Delbert E. Gantz Assistant ExaminerG. J. Crasanakis[57] ABSTRACT A depropanizer overhead from fractionation of an HFcatalyzed isoparaffin-olefin alkylation is partially condensed to form astream relatively poor in ethane and vapors relatively rich in ethane.The stream relatively poor in ethane is used as reflux and is pumped bya pump to a depropanizer-fractionator. Vapors rich in ethane arecondensed, contacted with liquid HF and are used as feed to an HFstripping zone. Bottoms from the stripping zone consisting essentiallyof ethane and propane to be yielded from the operation are flashed toform overhead ethane and propane yield and a bottoms propane stream poorin ethane and lean in HF and said stream poor in ethane and lean in HFis used as flush for said pump. HF stripper overhead is at least in partcondensed, two liquid phases are formed, the acid phase is removed andthe hydrocarbon phase is returned as reflux to the stripper and/or theoverhead is at least in part condensed and the condensate thus obtainedintermingled with the condensate obtained when condensing the vaporsrich in ethane; phases are formed, and acid phase formed is separatedand hydrocarbon phase is used as feed to the stripping zone. A pump isprovided to draw from an extractor-settler HF acid settled therein andto admix therewith either or both the condensates obtained uponcondensing the ethane rich vapor and that obtained upon condensing HFstripper overhead, thus intermingled liquids are passed to saidextractorsettler from which an acid phase formed is separated andhydrocarbon phase formed is passed to the stripping operation. Flush forthe pump is provided by the propane lean in ethane and lean in HF.

6 Claims, 1 Drawing Figure PUMP FLUSH FRACTIONATION OF EFFLUENT FROM HFCATALYZED ALKYLATION This invention relates to the alkylation of anisoparaffin with an olefin in the presence of HF acid. It also relatesto the fractionation of an. alkylation effluent obtained from the HFcatalyzed alkylation of an isoparaffin with an olefin.

In one of its concepts the invention provides for the fractionation ofan HF-catalyzed alkylation effluent to obtain a depropanizer overheadvapor containing ethane, propane, HF and organic fluorides. The overheadis partially condensed forming a liquid rich in propane and and lean inethane. Said liquid is pumped with a pump as reflux to the depropanizer.The ethane rich vapor containing HF thus remaining is condensed, liquidacid is separated therefrom, and a liquid hydrocarbon phase thusobtained is passed to an HF stripping operation wherefrom a bottomsconsisting essentially of ethane and propane are obtained. The bottomsare flashed to obtain a vaporous ethanepropane yield, and a bottomsessentially consisting of propane poor in ethane and lean in HF, andsaid bottoms are used as flush for said pump. In another of its conceptsthere is provided in an operation as just described a recontacting ofthe stream obtained when the ethane rich vapors are condensed with an HFacid phase separated upon the partial condensation of the depropanizeroverhead thus to remove organic fluorides from said ethane rich streaminto the acid. Still further, in another concept there is provided acondensing of overhead from the HF stripping, containing HF, ethane, andpropane, and the condensate thus obtained is admixed with the liquidobtained upon condensing said ethane rich vapor obtained upon saidpartial condensing. In a further concept still the thus admixed liquidsare pumped and further admixed as in an eductor with liquid HF takenfrom an extractor-settler and the thus admixed liquids are passed tosaid extractor-settler from which a liquid acid phase is removed andfrom which hydrocarbon phase is passed to said HF stripping operation.Further still according to a concept of the invention the HF stripperoverhead is cooled condensed forming an acid phase which is recoveredand a hydrocarbon phase which is returned to the stripper as refluxtherefore.

Considering the energy shortfall, which is now extant and which has beenbuilding for some years and which is becoming increasingly critical andwhich will be in existence for a number of years, it is imperative toseek to improve operations wherewith to save energy. Further, whereverthere is a process requiring venting of nonconde'nsables as when ethanein the feed to an alkylation is significantly above one percent of thepropane volume in the feed there results a problem in that there is lossof HF acid in the venting, and the concomitant energy which has beenrequired to produce the same. Further this loss causes a degree ofpollution and/or requires costly treatment of the gases or vapors tosequester the acid. Still further it is desirable to reduce the pressureat which fractionation is accomplished because of the cost offractionating equipment the thickness of which and the energy to producewhich considerably increases in proportion to the pressure at whichoperation is needed to be conducted.

l have now conceived of a combination of steps in which itis possible tolower considerably the pressure at which a depropanizer is operated.Thus 1 have conceived that if the depropanizer overhead is onlypartially condensed I can obtain therefrom a liquid hydrocarbon phase orpropane-rich stream quite lean in ethane and that this stream can bepumped as reflux to the depropanizer operation which now can be operatedat a lower pressure than conventionally. Further, according to myconcept, I provide for the condensing of the thus obtained ethane-richvapors, separtion of liquid HF acid therefrom upon settling to form aliquid acid phase, and then stripping in an HF stripping operation thehydrocarbon phase remaining to obtain a stripped bottoms which containthe ethane-propane yield, which then are flashed to obtainethane-propane yield from the operation, and a flashed liquid bottomsconsisting essentially of propane and lean in ethane and lean in HFwhich is used for pumped flush. Further, I have conceived relatedoperations as described herein.

An object of this invention is to provide an improved process for thealkylation of an isoparaffin-olefin. A further object of the inventionis to provide a process for the fractionation of the effluent from an HFcatalyzed alkylation of an isoparaffin and an olefin. Further still anobject of the invention is to provide a lower pressure fractionation fordepropanizing an alkylation effluent as herein described. Still furtheran object of the invention is to provide a reflux for a depropanizingoperation the reflux being lean in ethane. Further still an object ofthe invention is to provide a pump flush consisting essentially ofpropane lean in ethane and lean in HF. A further object still is toprovide a combination operation in which organic fluorides are recoveredin an acid phase. A still further object of the invention is to providean improved HF stripper feed processing. Another object still is toprovide an improved HF stripper operation. lmportantly, another objectis to provide for the reduction in cost of equipment and cost ofoperation. Also, importantly, an object of the invention is to reduceenergy requirements to produce and to operate equipment required for thealkylation of an isoparaffin with an olefin in the presence of HF acid.Another important object of the invention is to reduce losses ofexpensively obtained HF acid catalysts.

Aspects, concepts, objects and the several advantages of the inventionare apparent from a study of this disclosure, the drawing and theappended claims.

According to the present invention, there is provided an alkylationoperation for alkylating an isoparaffin with an olefin, e.g., isobutaneand/or isopentane with at least one of ethylene, propylene, a butylene,an amylene and a hexylene, wherein in the alkylation hydrocarboneffluent there are present ethane, propane, normal butane, isobutane,organic fluorides and heavier hydro-' carbons including alkylate boilingrange hydrocarbons, and HF catalyst, and wherein the effluent isfractionated in a fractionation zone to remove therefrom a vapor streamrich in ethane, propane and HF, and organic fluorides, the steps incombination which comprise partially condensing said stream to form afirst liquid hydrocarbon phase rich in propane and relatively lean inethane and a first acid phase and using at least a portion of said firstliquid hydrocarbon phase by pumping the same with a pump as reflux forsaid fractionation zone, thereby being able to operate saidfractionation zone at a pressure significantly lower than when theoverhead therefrom is not treated to reduce the ethane contents thereofas herein described.

Further according to the invention, there is provided an operation as isdescribed wherein upon said partial condensing results a vapor streamrelatively rich in ethane and containing propane, HF and organicfluorides, said vapor stream is condensed to form a second liquid phasecontaining propane, HF and organic fluorides and relatively rich inethane, said second liquid phase is settled to form and separatetherefrom a second liquid acid phase leaving a second liquid hydrocarbonphase, said second liquid hydrocarbon phase is passed to an HF strippingZone, in said stripping zone there is removed a stripped bottomsconsisting substantially of only ethane and propane, said bottoms areflashed obtaining ethane and propane vapors yielding a flashed liquidbottoms stream lean in ethane and lean in HF, and consisting essentiallyof propane and using said stream as flush for the reflux pump, and forthe charge pump for the HF stripper.

Other features of the invention are apparent from this disclosure andare claimed as in the appended claims.

Generally, there are known in the art the conditions for the alkylationof an isoparaffln with an olefin, the alkylation resulting in analkylation effluent which is fractionated. The description of thedrawing will be made in connection with an effluent containinghydrocarbons boiling in the alkylate gasoline boiling point range,normal butane, isobutane, ethane, propane, HF and organic fluoridestogether with some noncondensables which if not vented will accumulatein the equipment.

Referring now to the drawing, an alkylate containing effluent feed ispassed to fractionator 11 from which there are removed an alkylateproduct bottoms 13, a side stream of vaporous normal butane 12, a sidestream of isobutane vapor l4, and from above the feed, an isobutaneliquid stream 15 as well as an overhead vapor stream 16 containingprincipally ethane, propane, HF and organic fluorides. Stream 16 ispartially condensed at 17 and passed into accumulator 18 in which liquidhydrocarbon and liquid acid phases are formed, and from which a vaporrich in ethane 21 is taken off and passed to condenser 22 and thereincon densed. Liquid propane lean in ethane is pumped by the pump and fromaccumulator 18 to the top portion of the fractionator 11 as refluxtherefor. According to the invention, by supplying an ethane-leanpropane reflux the pressure in the fractionator or depropanizer can beconsiderably lower than conventional, as earlier noted.

Acid phase is separated at 19 from the leg of accumulator 18 and can bereturned to the alkylation unit for reuse as a catalyst in thealkylation reaction. This is shown at 34 and 35. However, in theembodiment now described the separated acid is recombined with thecondensate from condenser 22 passed by 23, 25, 26 and pump 27 to eductor28 whence it is passed by 30 into extractor-settler 31. Phases areformed in extractor-settler 31, a lower liquid acid phase being drawninto eductor 28 by 29 and an upper liquid hydrocarbon phase being passedby 36 and 38 to HF stripper 39 having bottoms reboiler 40. A portion ofthe hydrocarbon phase taken through 36 can be passed by 24 into pipe 25for further contacting with acid as just described. Bottoms 41 from HFstripper 39 consist essentially of the ethane-propane which is passedthrough heater 42 and flashed in tank 43 yielding overhead vapor at 47which is condensed at 48 to produce the liquid yield 49 of ethane andpropane from the process. This yield is passed to an operation (notshown) to remove residual fluoride therefrom. Bottoms liquid 44 fromflash tank 43 are passed by cooler 37 and used as pump flush by way of46 and 45. The use of pump flush, generally, is known in the art.According to a feature of this invention the pump flush is lean incorrosive HF and lean in ethane and therefore, significantly, the refluxat 20 does not add any real significant quantity of ethane tothefractionation operation, nor corrosive HP in the pump flush.Similarly the operation of HF stripper 39 is considerably improvedbecause the flush to pump 27 does not recycle any really significantportion of ethane to the stripper.

'The overhead from stripper 39 is at least in part treated by at leastone of the following alternates.

Overhead 50 is passed by conduit 55 to condenser 56 and to phaseseparator 57 from the bottom of which a liquid acid phase 58 is removedand returned to alkylation as earlier discussed for stream 35.Noncondensables, if any, are vented from the top of 57, and liquidhydrocarbon phase taken through 59 as reflux for stripper 39.

Alternately, at least a portion 51 of the HF stripper is condensed at 52liquid accumulating in accumulator 53. Accumulator 53 is provided with arefrigerated vent gas release. Liquid from accumulator 53 is passed by54 into 26 and thence to pump 27 for admixture with the hydrocarbons andacid which are contacted by vigorous intermixing at 28, pass via conduit30 into 31, and separate into two liquid phases in extractor-settler 31,as already described.

The addition of stripper feed pump 27, in the apparatus described, willallow the propane yield to contain from about 2 up to about 10 percentethane. The pump suction flow is the net volume of propane-ethane fromthe depropanizer overhead to be yielded out the bot tom of the stripperplus the stripper overhead. The HF stripper bottoms are made up of thenet propaneethane yield plus two pump flushes. The flash on the stripperbottoms will further increase the ethane content of the yield and reducethe amount of ethane that otherwise would be recycled in the pump flushand be recovered in the bottoms.

It is within the broad scope of the invention to pass the vapor stream21, even as a vapor in part or all of it directly to the HF stripper.

Depending upon the feedstock, catalyst and other characteristics of aparticular operation, as one skilled in the art in possession of thisdisclosure will understand, the specific conditions of operation givenbelow can vary within the approximate ranges which are also given.

continued,

. CALCULATED OPERATION- Approximate b. condensing said first vaporstream to form a second liquid phase containing propane, HF- and.organic'fluorides-and relatively rich in ethane,

,T i l Ranges 0. settling said second. liquid phase to form and to Bommtemperature): 1 l 41 150 separate therefrom a second acid phase from aPressure, psia 330 280 430 second llquld hydrocarbon phase, 57 andAccumulator 01. passing said second liquid hydrocarbon phase to anemperature, "F 100 60 l25 pressure psia 325 275 425 HF stripping zone,in said stripping zone removmg Flash Unit 43: a stripped bottomsconsisting substantially of only Temperature, "F 142 I20 150 Pressure,psia 325 275 425 etharie P e. flashing sa1d stripped bottoms to removetherefrom a second vapor stream containing ethane and pro- In the tablebelow there are given the compositions of Pane thus g f gaggshechbottoms stream lean m the principal streams in the process forthe typical h fg i an I th operating conditions above Set out f. usingsai as e ottoms stream can 1n e ane,

TABLE Barrels Per Day Stream l0 l2 l3 l4 l5 16 21 25 38 41 44 47 5O 5958 Composition Ethane & Lighter 34 2 5 200 27 27 76 29 43 24.7 47 47Propane 2147 583 873 12642 834 834 1247 977 287 69] 270 270 lsobutane20557 18 4 9888 10646 339 5 5 9 8 l l l l Normal Butane 4142 299 1841925 1734 3 Pentanes Plus 3685 25 3370 l90 I00 HF 195 266 34 160 9 Nil(.004) 8.9 2.48 6.42 160 and lean in HF, a flush for said pump in step(a), Reasonable variation and modification are possible whereby theintermingling of the flush from the within the scope of the foregoingdisclosure, drawing, pump with said reflux will not significantly addand the appended claims of the invention the essence 3O ethane to saidreflux and therefore to said fractionof which is that there have beenprovided an improved, considerably less energy-consuming over allalkylation of an isoparaffin with an olefin in the presence of HF acidincluded in the concept of which are partial condensing to obtain anethane-lean propane reflux thus to permit operation of the depropanizerzone at a lower pressure than usual, steps in combination to produce anethane lean and HF lean propane flush for the reflux pump and otherpumps in the operation thus avoiding corrosion and also the return ofethane to the system, the combination of steps in connection with the HFstripper as described in treating the overhead as well as the bottomsthus to reduce ethane venting and HF loss, to increase the ability ofthe operation to produce ethane in the propane yield thus reducing it inthe operation having set forth substantially as described.

I claim:

1. In an alkylation operation of which an isoparaffin is alkylated withan olefin and wherein in the alkylation effluent there are presentethane, propane, butane, isobutane, organic fluorides and heavierhydrocarbons including alkylate boiling range hydrocarbons, and HFcatalyst, and wherein the effluent is fractionated in a fractionationzone to remove therefrom a stream rich in ethane, propane, and HF, andorganic fluorides, the steps in combination which comprise a. partiallycondensing said stream to form a first liquid hydrocarbon phase rich inpropane and relatively lean in ethane, a first vapor stream relativelyrich in ethane and containing propane, HF and organic fluorides, and afirst acid phase and using at least a portion of said first liquidhydrocarbon phase by pumping the same with a pump as reflux for saidfractionation zone, thereby operating said fractionation zone at apressure significantly lower than when the overhead therefrom is nottreated to remove the ethane content thereof as herein described,

ation zone.

2. An operation according to claim 1 wherein said second liquid phasecontaining propane, HF and organic fluorides and relatively rich inethane is intermingled with said first acid phase, thus to reduce saidorganic fluorides in said second liquid phase, the intermingled phasesare settled to form a third acid phase which is separated from theoperation and a third hydrocarbon phase and said third hydrocarbon phaseis passed to said stripping zone.

3. An operation according to claim 2 wherein said third hydrocarbonphase is passed to said stripping zone with a pump and a portion of saidflashed bottoms stream lean in ethane and lean in HF, is used as a flushfor said pump whereby the intermingling of the flush from said pump withsaid third hydrocarbon phase will not significantly add ethane to saidthird hydrocarbon phase thereby increasing significantly the efficiencyof the stripping and of the removal of ethane from the operation.

4. An operation according to claim 2 wherein the stripping zone overheadcontaining HF, ethane and propane is at least in part condensed, thereare formed an acid phase which is separated and a hydrocarbon phasewhich is returned to the stripping zone as reflux therefor.

5. An operation according to claim 2 wherein the stripping zone overheadcontaining HF, ethane and propane is at least in part condensed and thecondensate is combined with said second liquid phase containing propane,HF, organic fluorides and which is relatively rich in ethane.

6. An operation according to claim '1 wherein said second liquid phasecontaining propane, HF, organic fluorides and relatively rich in ethaneis comingled with said first acid phase and wherein the thus comingledliquids are vigorously admixed with HF acid supplied from anextractor-settling zone, the final admixture 3,929,924 8 thus obtained[8 passed into said extractor-settling is removed and wherein ahydrocarbon phase f d zone thus extractin into said HF acid the or anicfluorides in Said Secognd liquid Phase Said final m saidextractor-settling zone 18 passed to said stripping ture being settledin said extractor-settling zone, an HF Zone as the feed therefor acidphase containing said extracted organic fluorides

1. IN AN ALKYLATION OPERATION OF WHICH AN ISOPARAFFIN IS ALKYLATED WITHAN OLEFIN AND WHEREIN IN THE ALKYLATION EFFLUENT THERE ARE PRESENTETHANE, PROPANE, BUTANE, ISOBUTANE, ORGANIC FLUORIDES AND HEAVIERHYDROCARBONS INCLUDING ALKYLATE BOILING RANGE HYDROCARBONS, AND HFCATALYST, AND WHEREIN THE EFFLUENT IS FRACTIONATED IN A FRACTIONATIONZONE TO REMOVE THEREFROM A STREAM RICH IN ETHANE, PROPANE, AND HF, ANDORGANIC FLUORIDES, THE STEPS IN COMBINATION WHICH COMPRISE A. PARTIALLYCONDENSING SAID STREAM TO FORM A FIRST LIQUID HYDROCARBON PHASE RICH INPROPANE AND RELATIVELY LEAN IN ETHANE, A FIRST VAPOR STREAM RELATIVELYRICH IN ETHANE AND CONTAINING PROPANE, HF AND ORGANIC FLUORIDES, AND AFIRST ACID PHASE AND USING AT LEAST A PORTION OF SAID FIRST LIQUIDHYDROCARBON PHASE BY PUMPING THE SAME WITH A PUMP AS REFLUX FOR SAIDFRACTIONATION ZONE, THEREBY OPERATING SAID FRACTIONATION ZONE AT APRESSURE SIGNIFICANTLY LOWER THAN WHEN THE OVERHEAD THEREFROM IS NOTTREATED TO REMOVE THE ETHANE CONTENT THEREOF AS HEREIN DESCRIBED, D.CONDENSING SAID FIRST VAPOR STREAM TO FORM A SECOND LIQUID PHASECONTAINING PROPANE, HF AND ORGANIC FLUORIDES AND RELATIVELY RICH INETHANE, C. SETTLING SAID SECOND LIQUID PHASE TO FORM AND TO SEPARATETHEREFROM A SECOND ACID PHASE FROM A SECOND LIQUID HYDROCARBON PHASE, D.PASSING SAID SECOND LIQUID HYDROCARBON PHASE TO AN HF STRIPPING ZONE, INSAID STRIPPING ZONE REMOVING A STRIPPED BOTTOMS CONSISTING SUBSTANTIALLYOF ONLY ETHANE AND PROPANE, E. FLASHING SAID STRIPPED BOTTOMS TO REMOVETHEREFROM A SECOND VAPOR STREAM CONTAINING ETHANE AND PROPANE, THUSYIELDING A FLASHED BOTTOMS STREAM LEAN IN ETHANE, AND LEAN IN HF, AND F.USING SAID FLASHED BOTTOMS STREAM LEAN IN ETHANE, AND LEAN IN HF, AFLUSH FOR SAID PUMP IN STEP (A), WHEREBY THE INTERMINGLING OF THE FLUSHFROM THE PUMP WITH SAID REFLUX WILL NOT SIGNIFICANTLY ADD ETHANE TO SAIDREFLUX AND THEREFORE TO SAID FRACTIONATION ZONE.
 2. An operationaccording to claim 1 wherein said second liquid phase containingpropane, HF and organic fluorides and relatively rich in ethane isintermingled with said first acid phase, thus to reduce said organicfluorides in said second liquid phase, the intermingled phases aresettled to form a third acid phase which is separated from the operationand a third hydrocarbon phase and said third hydrocarbon phase is passedto said stripping zone.
 3. An operation according to claim 2 whereinsaid third hydrocarbon phase is passed to said stripping zone with apump and a portion of said flashed bottoms stream lean in ethane andlean in HF, is used as a flush for said pump whereby the interminglingof the flush from said pump with said third hydrocarbon phase will notsignificantly add ethane to said third hydrocarbon phase therebyincreasing significantly the efficiency of the stripping and of theremoval of ethane from the operation.
 4. An operation according to claim2 wherein the stripping zone overhead containing HF, ethane and propaneis at least in part condensed, there are formed an acid phase which isseparated and a hydrocarbon phase which is returned to the strippingzone as reflux therefor.
 5. An operation according to claim 2 whereinthe stripping zone overhead containing HF, ethane and propane is atleast in part condensed and the condensate is combined with said secondliquid phase containing propane, HF, organic fluorides and which isrelatively rich in ethane.
 6. An operation according to claim 1 whereinsaid second liquid phase containing propane, HF, organic fluorides andrelatively rich in ethane is comingled with said first acid phase andwherein the thus comingled liquids are vigorously admixed with HF acidsupplied from an extractor-settling zone, the final admixture thusobtained is passed into said extractor-settling zone, thus extractinginto said HF acid the organic fluorides in said second liquid phase,said final admixture being settled in said extractor-settling zone, anHF acid phase containing said extracted organic fluorides is removed,and wherein a hydrocarbon phase formed in said extractor-settling zoneis passed to said stripping zone as the feed therefor.